1. Technical Field of the Invention
The invention relates generally to the communication devices; and, more particularly, it relates to the field of amplification that may be implemented within such communication devices.
2. Description of Related Art
High speed wideband data amplifiers are used in wideband data communication applications. For a number of reasons including speed limitations of process technology, power consumption and other cost related concerns, it is desirable to develop efficient techniques to boost the amplifier bandwidth for higher frequency operations. High speed circuit techniques such as current-controlled CMOS (or C3MOS) logic have been developed that have brought about marked increase in the speed of circuitry fabricated using standard CMOS process technology.
Moreover, when implementing such circuitry onto silicon substrates and into packages (e.g., within integrated circuits), there is oftentimes a difficulty in the interfacing that is performed between the initial circuitry within an integrated circuit and the bond wires, traces, and/or pads to which this initial circuitry within the integrated circuit communicatively couples. This interface may generally be referred to as the interface between a silicon chip and a package and/or circuit board. Generally speaking, there is oftentimes a difficulty in the impedance matching at this critical interface. In doing this interfacing stripline and microstrip transmission lines may be employed.
Stripline and microstrip transmission lines are transverse electromagnetic (TEM) and quasi-TEM structures, respectively. Ideally, waves that propagate on these structures have propagation constants that are predominantly linear with frequency and hence phase velocities that are nearly constant with frequency. In isolation, these lines exhibit a single-ended characteristic impedance, phase velocity and attenuation. For instance, if a transmission line with 50Ω characteristic impedance is terminated with a 50Ω load, there will be no reflection at the interface between the transmission line and the load.
However, in real life applications, several non-linearities create impedance mismatch at the interface between the silicon chip and package and/or circuit board, which may cause significant reflection and thus degrade the signal integrity. Firstly, as a pair of these striplines and microstrip transmission lines is moved closer together, for example, at the package substrate, coupling occurs that significantly alters the transmission parameters and makes possible the propagation of differential and common-mode guided waves. To preserve signal integrity, both differential and common-mode reflection needs to be minimized. Secondly, the bonding wire connecting package to silicon die usually exhibit inductive impedance at multi-GHz (Giga-Hertz) data rates. Thirdly, the capacitive loading to the signal path from bonding pad and ESD (Electrostatic Sensitive Device) structure at the silicon die becomes more and more significant as the data rate increases, even if termination resistors are placed very close to the input pads. Furthermore, the capacitive loading from the transistors at the input of the data amplifier creates shorts in parallel with the termination resistor and reduces the overall impedance at higher frequency, which results in reduced bandwidth of the input data amplifier and increased reflection at input. In a single-ended configuration represented by lumped elements, the mismatch at the interface of silicon 120 and package and/or circuit board 110 can be shown in FIG. 1.
FIG. 1 illustrates a prior art embodiment of impedance mismatch 100 at the interface of silicon 120 and package and/or circuit board 110.
At the interface, looking towards the package and/or circuit board side 110, the impedance is predominantly inductive. In contrast, looking towards the silicon side 120, the impedance is predominantly capacitive. This is true for both differential mode and single-mode transmission.
There continually exists in the art a need for amplifier stages having a frequency response that gives sufficient gain at the higher frequency ranges while also minimizing the power consumption of the amplifier, and for eliminating expensive process requirements.